The present invention pertains to AV synchronous cardiac pacing systems, and particularly to delivering multi-site ventricular pacing triggered by a ventricular sense event detected at any ventricular site during the AV delay, particularly delivering pace pulses to the right and left ventricles triggered by a ventricular sense event in either the right or left ventricles during the AV delay only.
In diseased hearts having conduction defects and in congestive heart failure (CHF), cardiac depolarizations that naturally occur in one upper or lower heart chamber are not conducted in a timely fashion either within the heart chamber or to the other upper or lower heart chamber. In such cases, the right and left heart chambers do not contract in optimum synchrony with each other, and cardiac output suffers due to the conduction defects. In addition, spontaneous depolarizations of the left atrium or left ventricle occur at ectopic foci in these left heart chambers, and the natural activation sequence is grossly disturbed. In such cases, cardiac output deteriorates because the contractions of the right and left heart chambers are not synchronized sufficiently to eject blood therefrom. Furthermore, significant conduction disturbances between the right and left atria can result in left atrial flutter or fibrillation.
It has been proposed that various conduction disturbances involving both bradycardia and tachycardia of a heart chamber could benefit from pace pulses applied at multiple electrode sites positioned in or about a single heart chamber or in the right and left heart chambers in synchrony with a depolarization which has been sensed at least one of the electrode sites. It is believed that cardiac output can be significantly improved when left and right chamber synchrony is restored, particularly in patients suffering from dilated cardiomyopathy and CHF.
A number of proposals have been advanced for providing pacing therapies to alleviate these conditions and restore synchronous depolarization and contraction of a single heart chamber or right and left, upper and lower, heart chambers as described in detail in commonly assigned U.S. Pat. Nos. 5,403,356, 5,797,970 and 5,902,324 and in U.S. Pat. Nos. 5,720,768 and 5,792,203 all incorporated herein by reference. The proposals appearing in U.S. Pat. Nos. 3,937,226, 4,088,140, 4,548,203, 4,458,677, 4,332,259 are summarized in U.S. Pat. Nos. 4,928,688 and 5,674,259, all incorporated herein by reference. The advantages of providing sensing at pace/sense electrodes located in both the right and left heart chambers is addressed in the ""688 and ""259 patents, as well as in U.S. Pat. Nos. 4,354,497, 5,174,289, 5,267,560, 5,514,161, and 5,584,867, also all incorporated herein by reference.
The medical literature also discloses a number of approaches of providing bi-atrial and/or bi-ventricular pacing as set forth in: Daubert et al., xe2x80x9cPermanent Dual Atrium Pacing in Major Intra-atrial Conduction Blocks: A Four Years Experiencexe2x80x9d, PACE (Vol. 16, Part II, NASPE Abstract 141, p. 885, April 1993); Daubert et al., xe2x80x9cPermanent Left Ventricular Pacing With Transvenous Leads Inserted Into The Coronary Veinsxe2x80x9d, PACE (Vol. 21, Part II, pp. 239-245, January 1998); Cazeau et al., xe2x80x9cFour Chamber Pacing in Dilated Cardiomyopathyxe2x80x9d, PACE (Vol. 17, Part II, pp. 1974-1979, November 1994); and Daubert et al., xe2x80x9cRenewal of Permanent Left Atrial Pacing via the Coronary Sinusxe2x80x9d, PACE (Vol. 15, Part II, NASPE Abstract 255, p. 572, April 1992), all incorporated herein by reference.
In the above-incorporated ""324 patent, an AV synchronous pacing system is disclosed providing three or four heart chamber pacing through pace/sense electrodes located in or adjacent one or both of the right and left atrial heart chambers and in or adjacent to the right and left ventricular heart chambers. During an AV delay and during a V-A escape interval, a non-refractory ventricular sense event detected at either the right or left ventricular pace/sense electrodes starts a conduction delay window (CDW) timer. A ventricular pace pulse is delivered to the other of the left or right ventricular pace/sense electrodes at the time-out of the CDW if a ventricular sense event is not detected at that site while the CDW times out.
In certain patients, it is undesirable to deliver ventricular triggered pacing in response to a non-refractory ventricular sense event detected during the time-out of the V-A escape interval. Such ventricular sense events are detected from premature ventricular contractions (PVCs) that disrupt the normal synchronous contraction of the atria and ventricles. In some cases, the application of triggered ventricular pace pulses can be beneficial, but in other cases, the ventricular pace pulses may be pro-arrhythmic, that is, likely to trigger a tachyarrhythmia.
In certain dual chamber pacemakers, ventricular safety pacing (VSP) window of 110 msec (or a programmed PAV delay if less than 110 msec) is commenced with the PAV delay. A ventricular sense event occurring after time-out of the VSP window, but during the remaining period of the AV delay, simply terminates the AV delay and restarts the V-A escape interval. However, a ventricular sense event detected during the VSP window causes a ventricular pace pulse to be delivered to the single ventricular pacing site at the time-out of the 110 msec VSP window. At the same time, the AV delay is terminated and the V-A escape interval is restarted. The delivery of the ventricular sense event detected at the time-out of the 110 msec VSP window is intended to ensure that ventricular pacing is provided in cases where noise detected across the ventricular pace/sense electrodes due to the delivered atrial pace pulse would otherwise inhibit ventricular pacing. If the detected ventricular sense event is a true ventricular depolarization, the ventricular pace pulse is delivered harmlessly into the refractory period at that site in the ventricle rather than the following vulnerable period.
This delayed delivery of the ventricular pace pulse in the VSP triggered ventricular pacing mode is inappropriate under certain circumstances where patients would benefit from immediate triggered pacing during the AV delay.
Problems have been found with inappropriate location of sensing electrodes in patients with particularly long QRS waveforms. We believe that ventricular sensing may be enabled at only one particular chosen site or at a different site to avoid such problems. Particularly, both the mistaken double sensing of a single depolarization and polarization-induced sense amplifier blanking when inappropriate may be avoided by being able to determine where the device will sense the depolarization wavefront to the extent possible with the several electrodes available in multi-site systems. For example, if a depolarization has started well before it is sensed and has traversed one of the pacing electrodes several milliseconds (ms) earlier, pacing as soon as possible is preferred over waiting the 110 ms after sensing at the chosen but second to sense electrode. In thinking about how to appropriately enable particular sense electrodes, we have also found that the use of trigger pacing during the AV delay may be preferred over standard ventricular safety pacing for systems that employ more than one pace/sense electrode in the ventricle. In preferred embodiments this triggering would occur only after an atrial pace (not an atrial sense) to make it more specifically a safety feature.
As we have begun to describe it, there is a need for an optimized AV sequential, multi-site ventricular pacing system that provides ventricular triggered pacing throughout the AV delay and avoids precipitating arrhythmias at other times.
The present invention provides a pacing system for selectively sensing spontaneous ventricular cardiac depolarizations at first and second spaced apart ventricular sites during the time-out of an AV delay and delivering ventricular pace pulses to one or both of the spaced apart ventricular sites in a triggered pacing mode. The first and second ventricular sites are preferably right ventricular (RV) and left ventricular (LV) pace/sense electrode sites, and RV event and LV event signals are sensed at the RV and LV pace/sense electrodes. A V-A pacing escape interval is started upon a RV or LV sense event or a first ventricular pace pulse delivered upon time-out of the AV delay. A triggered ventricular pace pulse or pulses is delivered to one or both of the RV and LV pace/sense electrode sites upon detecting an RV sense event or LV sense event at any time during the AV delay. Triggered ventricular pacing is disabled during the V-A escape interval.
In a preferred triggered pacing mode, a first pace pulse is delivered without delay upon a RV or LV sense event, the triggered pacing delay is timed out, and a second pace pulse is delivered to the other one of the RV or LV pace/sense electrode sites after time-out of the triggered pacing delay. In another triggered pacing mode, a RV or LV pace pulse is delivered without delay upon a RV or LV sense event during the AV delay to one of the RV or LV pace/sense electrode sites.
The present invention provides optimized AV sequential, multi-site ventricular pacing system that delivers triggered ventricular pacing to one or more ventricular pacing sites at any time throughout the AV delay and avoids precipitating arrhythmias at other times.
The present invention is preferably implemented in AV synchronous pacing systems for providing atrial and ventricular bi-chamber pacing of at least one of the right and left atria and both the right and left ventricles. The present invention is preferably implemented into an external or implantable pulse generator and lead system selectively employing right and left heart, atrial and ventricular leads. The AV synchronous embodiments may be implemented into an IPG or external pulse generator and lead system providing right and left ventricular pacing and sensing and either both right and left atrial pacing or just right or left atrial pacing and sensing. Alternatively, the invention can be implemented in IPGs or external pulse generators and lead systems having hard wired connections and operating modes that are not as programmable.